[Aerkuld]

I just thought it might be worth posting this as it may help someone else out at some point.
Starting a few weeks ago I had a couple of isolated instances of PSM and ABS failure notification on the dash display followed by the warning lights being lit. I did note that it only happened as I was braking. However, after turning the car off and restarting there was no reoccurrence for a significant period of time. Now I know I should have taken it to a dealer for inspection but as my nearest dealer is at least a two hour drive and the fact that the fault occurred only twice with a significant period between events I put it off until the next time I would be in the area.
Well, last weekend I started to wish that I had taken it in as the fault was occurring every time I hit the brakes. Naturally this was a Sunday so there was no chance of getting it looked at that weekend so I decided to investigate further. I drove home and backed into the garage. As I came to a stop I noticed I didn’t have any brake lights. Following a little reading around I came to the conclusion that my brake pedal switch was the most likely culprit for both problems. It was very simple to remove, a quarter turn and it just pulls out the bracket mount. The switch appears to have two functions, one is to actuate the brake lights and the other is to send a “Brakes on” signal probably to the cruise control. I would guess that the ABS/PSM looks for both and if it finds one without the other it triggers a fault – don’t take this as gospel it’s just my speculation. You can check the switch by measuring the resistance across terminals 1&4 then 1&2 as marked on the contacts of the switch. 1&4 should be closed circuit (zero resistance) with the switch depressed and then open circuit once it is released (infinite resistance), while 1&2 works the opposite way around. You should easily be able to tell if it isn’t working correctly because one or both sets of contacts will not change no matter what you do with the switch or it may stick and give inconsistent results. This is what was happening with mine. I then took the switch apart and cleaned it and it did give me brake light operation but would still throw up faults. To cut a long story short I ended up ordering a new switch which I fitted today and I have had no fault signals since and I know my brake lights work. Be careful when refitting the switch though as it has a self adjusting mechanism built into it. Basically the plunger on the switch can ratchet so that the distance to the pedal is always set correctly. Make sure that when you fit the switch the plunger is pulled out as far as it will go, then fit the switch into the bracket with the brake pedal pushed down. Once the switch is in the bracket give it a quarter turn to lock it in then release the pedal and the switch adjustment is automatic.
I am planning on visiting my dealer this weekend to get confirmation that everything is as it should be and to get any fault codes in the computer verified and cleared but it would appear that the problem is fixed. A new brake pedal switch is all it needed!
For reference my old switch has a part number of 996.613.113.01 but the new switch has a part number of 996.613.113.02 which I would suppose is a later revision.